1. Field of the Invention
The present invention relates to a communication apparatus, a communication system, a communication method, and a storage medium.
2. Description of the Related Art
General widely used Internet standard techniques include protocols such as Hyper Text Transfer Protocol (HTTP) and User Datagram Protocol (UDP). In some protocols, such as HTTP/2 as a new version of HTTP for which the specification is currently being defined, processing for upgrading the version of the currently used protocol is executed at the time communications start. This upgrade is achieved with a communication parameter, defined in the specification of the protocol, exchanged between communication apparatuses so that a communication parameter, required for the communications using the protocol, is set in the communication apparatuses.
In this context, a method of establishing a plurality of Transmission Control Protocol (TCP) connections, and performing a plurality of HTTP communications in parallel achieve communications at higher speed has been proposed as discussed in Japanese Patent Application Laid-Open No. 2012-95098.
However, a configuration discussed in Japanese Patent Application Laid-Open No. 2012-95098 has a problem in that reestablishment of a communication path requires the upgrade processing for a protocol used for communications, and thus requires a long period of time for reestablishment the communication path. For example, there arises a problem that the reestablishment of a communication path requires a long period of time occurs when a communication error occurs after a connection is established as communication path for HTTP/2 and reestablishment of the connection starts from the protocol upgrade processing.
When the communication parameter is, exchanged in the protocol upgrade processing, first communication apparatus might transmit, to a second communication apparatus, a communication parameter of an incorrect value that does not conform to the specification of the protocol, or a communication parameter of a value unacceptable by the second communication apparatus. In this case, the second communication apparatus needs to transmit a signal, indicating that communications need to be terminated due to the occurrence of the connection error, to the first communication apparatus, and then terminate the communication using the upgraded protocol. Unfortunately, this procedure has a problem of low connectivity between the communication apparatuses due to a failure to start normal communications, with the first communication apparatus transmitting the communication parameter of an incorrect value an unacceptable value again in an attempt reestablish the connection and start the communications using the upgraded protocol.